John Cairncross

John Cairncross (25 July 1913-8 October 1995) was a Scottish intelligence officer and spy who was a double agent of the United Kingdom and the Soviet Union during World War II. As one of the Cambridge Five, he helped both rival allies in defeating Nazi Germany, and his information was instrumental in winning the Battle of Kursk for the Soviets in 1943.

Biography
John Cairncross was born on 25 July 1913 in Lesmahagow, Scotland, in the United Kingdom. All three of his brothers became professors, and he took the British Civil Service exam and won first place. In 1939, Commander Alistair Denniston had Cairncross, Hugh Alexander, Peter Hilton, Keith Furman, Charles Richards, and Alan Turing travel to Bletchley Park at the start of World War II to attempt to crack Enigma, the coding system that allowed Nazi Germany to relay important messages across the fronts. Every day from six to midnight, they would attempt to crack the day's code, but when the bell struck midnight, all of their progress would be lost, as the German code would reset. Later, Turing gained the funding to construct a machine to crack Enigma from Winston Churchill and he was made the leader of the group; he fired Keith and Charles and recruited Joan Clarke into the group (her parents would not allow it, so Turing secretly communicated with her while she was posted to the nearby female clerks' office).

During this time, Cairncross secretly passed messages to the Soviet Union, who were allies of the United Kingdom during the war against Germany, although Churchill did not trust them. Agent Stewart Menzies had secret knowledge of Cairncross' activities, but allowed him to send messages to the Soviets, as Churchill was too sensitive to do so himself; Cairncross' spying helped the Soviets to destroy the Nazis at the 1943 Battle of Kursk. The "Cambridge Five" of Soviet spies operated for both sides of the Allied Powers, benefitting both sides. Alan Turing eventually found out that Cairncross was a spy and threatened to report him, but Cairncross threatened to reveal his homosexuality, which was a crime in the United Kingdom and would result in the destruction of his beloved "Christopher" machine and all of his progress. The group eventually cracked the code, and they had to keep it secret so that the Germans did not decided to create a new code to replace Enigma. They helped in the Allied invasion of Europe, the Battle of the Bulge, and the fall of Germany by relaying German information to the Allies, and at the end of the war, they were forced to burn all evidence of their machine, and they had to return to school. Menzies reminded them that when they signed up, they agreed that everything that they did was top secret, and he told them to act as if they had never even heard the word "Enigma" or had worked with the government (they used the alibi of working in a "radio factory").

In 1951 he admitted to having spied for the Russians when MI5 found papers in Cambridge Five member Guy Burgess' apartment, and he was also believed to have leaked Manhattan Project details to the Soviets to help their nuclear program. Cairncross was never prosecuted for his spying, and he joined the treasury. He later worked as a translator for United Nations and from 1979 to 1995 he lived in France. Cairncross later returned to the United Kingdom, where he died at the age of 82.